A diplomatic source in Niger confirmed the ambush, saying that the attackers had come from Mali and had killed and injured several soldiers. Neither source could comment on whether any U.S. troops, who are stationed in the West African country at Agadez, had been killed.

WASHINGTON – U.S. investigators on Sunday returned to a village in Niger where four American soldiers were killed in an ambush in October carried out by Islamist militants, the military said. The news came a day after the Washington Post citing villagers reported that Sgt. La David Johnson, one of the four, was found with his arms tied and a gaping wound to the back of the head. The discovery suggested he was captured and executed. The investigative team, comprising U.S. and Nigerien officials, "returned to the village of Tongo Tongo, Niger, on Nov. 12 in order to gain a clearer understanding of the Oct. 4 ambush, the attack site and the surrounding environment, United States Africa Command (AFRICOM) said in a statement.

A military investigation has concluded that Army Sgt. La David T. Johnson died in a hail of gunfire, hit as many as 18 times as he took cover in thick brush during an October ambush in Niger. He fought to the end after fleeing militants who had just killed three comrades.

The U.S. Africa Command says it has sent a joint team with the Niger military to the village of Tongo Tongo to investigate the Oct. 4 attack by extremists that left four American and four Nigerien soldiers dead.

Islamist militants form part of a regional insurgency in the poor, sparsely populated deserts of West Africa's Sahel. Jihadists have stepped up attacks on U.N. peacekeepers, Malian soldiers and civilian targets since being driven back in northern Mali by a French-led military intervention in 2013.